Beneficiation of low-grade hematitic ore materials



BENEFICIATION OF LOW-GRADE HEMATITIC ORE MATERIALS Original Filed Sept.25, 1958 Nov. 13, 1962 F. D. DE VANEY 4 Sheets-Sheet 1 INVENTOR BY M win

14 ATTORNEYS 4 Sheets-Sheet 2 7////////////// ////A wA///// N k 0 6% a?!x mm \M O a a W 1.11/11! E Nov. 13, 1962 F. D. DE VANEY BENEFICIATION OFLOW-GRADE HEMATITIC ORE MATERIALS Original Filed Sept. 25, 1958BENEFICIATION OF LOW-GRADE HEMATITIC ORE MATERIALS Original Filed Sept.25, 1958 Nov. 13, 196 F. D. DE VANEY 4 Sheets-Sheet 3 INVENTOR g M: a .w

90 FM 2- & 7

ATTORNEY Nov. 13, 1962 F. D. DE VANEY 3,063,595

BENEFICIATION OF LOW-GRADE HEMATITIC ORE MATERIALS Original Filed Sept.25, 1958 4 Sheets-Sheet 4 INVENTOR B I M W M,

w ATTORNEY-5 United States Patent 3,063,695 BENEFICIATION 0F LGW-GRADEHEMATITIC ORE MATERIALS Fred D. De Vaney, Duluth, Minn., assignor to P-MAssociates, Cleveland, Ohio, a partnership Original application Sept.25, 1958, Ser. No. 763,348, now

Patent No. 2,931,720, dated Apr. 5, 1960. Divided and this applicationSept. 2, 1959, Ser. No. 837,757

1 Claim. (Cl. 266-20) The present invention relates to the beneficiationof lowgrade iron ore materials in which the iron values largely arepresent as non-magnetic oxides (and/ or hydroxides), e.g. hematite. Theinvention is particularly concerned with the beneficiation of such ironore materials in which the non-magnetic iron mineral is too fine grainedto be concentrated by gravity methods of concentration such assink-float, tabling, jigging, cyclone or the like.

Heretofore, a few of the cleanest fine-grained, lowgrade, essentiallynon-magnetic iron ore materials in which the predominant iron mineralWas crystalline specularite, have been concentrated by a procedureinvolving froth flotation. With such materials the flotation process hasbeen relatively successful. However, the majority of lean iron ores arenon-crystalline and cannot be effectively concentrated by the flotationprocess.

It has been found that the non-magnetic iron oxide contents of such orematerials can advantageously be concentrated by magnetically roastingthe crushed ore under conditions to convert substantially all-or atleast, the greater partof the non-magnetic oxidic iron content thereofto magnetite, grinding to fine particle size, and magneticallyseparating the magnetic portion from the non-magnetic tailing.

In accordance with the general principles of the present invention, themagnetic roasting step is carried out in a generally vertical,shaft-type'fu-rnace through which the coarsely crushed ore materialgravitationally descendscontinuously, or substantially continuously-as acontinuous column in counter flow to a current of a gas mixture having anet reducing effect and maintained at a controlled temperature. Said gasmixture comprises a major amount of carbon dioxide, nitrogen (and othernonoxidizing gaseous components of atmospheric air), and a relativelyvery small amount of an active reducing gas. of the group consisting ofhydrogen, carbon monoxide and a mixture of hydrogen and carbon monoxide.

This general process and apparatus for use in carrying it out have beendisclosed in U.S. Patents Nos. 2,528,552, 2,528,553 and 2,670,946 toPercy H. Royster.

According to the last two mentioned of these patents,

substantially all of the gas (i.e., gas mixture) passed in contactwith't-he column of ore was gas which had been, in unheated state,introduced adjacent the bottom of the latter. After a certain amount ofcounter-current flow through the ore columnduring which it became heatedto some extent by heat transfer from the orea part of this gas streamwas diverted from the column to a spatially separate mixing chamberwherein the diverted gas was mixed with highly heated, essentiallyneutral, gaseous combustion products whereby its temperature wasmaterially elevated, and the resulting hot mixture was reintroduced intothe 'ore columnat a level substantially above the level of diversion-tomingle with the undiverted part of the gas stream and with the latter totraverse the remainder of the ore column. This procedure, and, moreparticularly, the disclosed apparatus for effecting it, has acquired thedesignation of three-high process and three-high furnace, respectively,in that the furnace 3,063,695 Patented Nov. 13, 1962 included threerather well-defined parts serially arranged from top to bottom, namely,an uppermost part 1called the heating stove-in which the ore was heatedto the selected high temperature and at least to some extent reduced; anintermediate part 2-called the middle stovein which the hot ore frompart 1 was traversed only by the aforesaid undiverted portion of the gasstream and in which reduction was completed (in the event reduction hadnot already been completed in part 1 and a lowermost part 3called thecooling stove in which the reduced orewas cooled in contact with thefreshly introduced, unheated gas stream.

This three-high procedure was open to two main disadvantages. Firstly,the gas diverted at the top of part 3 of the furnace to the aforesaidmixing chamber was inherently dustladen and the entrained dust createdserious problems. Thus, dust carried by the diverted gas tended tosettle out in the flues between furnace part 1 and the mixing chamber,in the mixing chamber itself, and in the flues and ports between themixing chamber and the bottom of part 1 of the reducing furnace, and thebuild-up of such settled-out dust resulted in uneven flow of gases fromand to the furnace. the mixing chamber tended to clinker when subjectedto the highly heated gaseous combustion products, and clinker-formationwas distinctly disadvantageous if not actually dangerous. Experienceproved that removal of settledout dust from mixing chambers was a verytroublesome procedure. Measures for counteracting these dust problemswere only partially successful.

Secondly, the three-high procedure had the inescapable disadvantage thatthe distribution of the gases which traveled through the furnace properand the amount which was diverted to the mixing chamber varied widely,an exact split being impossible to attain. Such variation in split wasdue to changing pressures (e.g., changing.

pressures in the intermediate part 2 of the furnace) and to build-up ofsettled-out dust in the flues to and from the mixing chamber. For thesereasons, the furnace operation was incapable of close control. Forexample, while the temperature of the gas leaving the mixing chambercould be maintained constant, its volume was not sub-.

ject to exact control, and hence the total heat input to part 1 of thefurnace varied. Accordingly, the temperature of the gas stream passingthrough part 1 of the furnace fluctuated because of varying percentagesof relatively cold undiverted gas mixing with the relatively hotdiverted gas.

The process and apparatus of the present invention avoid theabove-mentioneddisadvantages and provide an improved procedure (styled a:twoahigh procedure) for magnetically roasting the hereinbeforedescribed ore materials. From the standpoint of structure, in thevertical shaft-type furnace per se of the present invention theabove-referred-to middle stove has been omitted entirely, the heatingstove being directly followed by the cooling stove, and likewise therehas been omitted any and all flues for diverting partially heated gasfrom the top of the cooling stove to the mixing chamber. From thestandpoint of process the spent gas, after having been cleaned andcooled and otherwise conditioned, is split into two fractional streams,one of which is conducted to the mixing chamber (wherein it is heated toa suitable elevated temperature without significant change incomposition, for introduction into the reducing furnace at the level ofthe bottom of the heating stove), and the other of which is-aftersuitable fortification with active reducing gasconducted to the bottomof the cooling stove.

Moreover, dust carried into Specifically, the procedure according to thepresent invention is carried out in the following manner: intermediatethe top and the bottom of the ore column there is introduced into thecolumn and caused to flow upwardly through the upper part of the columna current of nonoxidizing heating gas mixture different in chemicalcomposition from the spent gas mixture which exits from the top of theore column but differing from such spent gas in that, as introduced, itis at an elevated temperature of the order of from 800 to 1700- F.Simultaneously, there is introduced into the ore colnmnat a leveladjacent the bottom of the lattera current of a cold (i.e., unheated)reducing gas mixture comprising the gaseous constituents of said spentgas fortified" with a small addition of active reducing gas (CO, H or aCO-H mixture). This cold gas mixture, in being forced upwardly throughthe ore column, reduces any non-magnetic iron oxide (not alreadyreduced) to Fe O and simultaneously abstracts heat from the ore therebycooling the latter, and eventually mingles with the current of heatinggas mixture (introducedas stated above-at a level intermediate the topand the bottom of the column) and in admixture with the latter completesthe countercurrent passage through the remainder of the ore column andexits at the top as spent gas.

Because this spent gas still contains some residual active reducing gasvalues, the process is made essentially cyclic in character, in thefollowing manner: the spent gas, after having been diverted from the topof the furnace, and after having been slightly diminished in volume byventing a few percent to atmosphere-the amount of gas so vented beingequivalent to the gain in volume of the gases in the closed system due(a) to formation of water vapor from the moisture contained in the feedore and (b) to the addition of gaseous products of combustion of fuel inthe mixing chamber-45 cooled substantially to room temperature orthereabouts and simultaneously cleaned in a scrubber and then is splitinto two streams of unequal volume. The stream of smaller volume isforced through a mixing chamber wherein it is mixed with a stream ofsubstantially inert, non-oxidizing, high-temperature gas to form theaforesaid heating gas mixture which latter is introduced into the orecolumn adjacent the top and the bottom of the latter. The other,larger-volumed, stream is fortified by admixing with it a small amountof make-up gas rich in active reducing agent (CO, H or mixture thereof)which small amount is sufficient (l) to compensate in volume for thewasted spent gas and (2) to re-formulate the aforesaid current ofreducing gas mixture which is introduced-at about room temperature-intothe ore column at a level adjacent the bottom of the latter forcountercurrent flow therethrough.

The temperature and volume of the aforesaid heating gas mixture are soadjusted, and the ratio of said heating gas mixture to a unit volume ofcrushed ore materials is so maintained, that at the level ofintroduction of said mixture the ore material is heated to from 8 to1700 F. which temperature level slopes downwardly to an exit temperatureof the spent gas of about 200 F. (or somewhat higher) by reason of heatexchange between the hot gases and the ore material particles contactedby said gases (and which had been charged to the column at roomtemperature). 7

In the process just described, essentially all of the nonmagnetic oxidiciron of the charge column is reduced to R2 0, without, however, furtherreduction to FeO (or, to metallic iron). .Prevention of reduction beyondthe magnetite stage, in spite of the high temperature conditionsobtaining in the zone of major reduction, is assured by the presence inthe gases of a realtively very large amount of carbon dioxide gas orwater vapor or a combination of the two. It heretofore had beenconsidered necessary, when reducing with a gas rich in hydrogen, tomaintain a relatively low temperature in order to avoid over-reductionbeyond the Fe O level.

It will be appreciated, from the foregoing description, that the presentinvention avoids some or all of the abovediscussed disadvantagesinherent in the operation of a three-high reducing furnace of thevertical shaft type. By not diverting partially heated gas from thefurnace per se to the mixing chamber one eliminates dust from the mixingchamber and from the fines and ports leading from the latter to theheating stove" part of the reducing furnace; likewise, one entirelyeliminates any and all fines leading from the reducing furnace and,hence, entirely avoids material settling problems relative to suchflues. Equally importantly, by the present invention one attains theability exactly to control the distribution of the gases to the bottomof the cooling stove and to the mixing chamber in any desiredproportion: thereby, the optimum amount of gas can be distributed toeach point. The resulting exact distribution of gas makes it possiblemuch more uniformly to control the temperatures obtaining in the heatingstoveboth gas temperature and gas volume being subject to closecontroland hence to secure efi'icient roasting.

As 'will be appreciated, this procedure is best suited to processing arelatively coarse material-e.g., an ore material which has been crushedto l inch-in order to maintain good gas flow and to minimize backpressure. Coneqnently, for best operation the charge material shouldcontain a minimum of minus 10-14 mesh material. If the crusher productis relatively coarse and does not contain appreciably more than 10% offines (i.e., particles finer than 10-14 mesh), the entire crusherproduct can be charged to the ore column. If, however, the crusherproduct contains larger amounts of the fines, it is expedient either (1)to screen out the fines and to magnetically roast them by a differentprocess (e.g. by a fiuosolids procedure) or (2) to agglomerate them bythe known techniques such as balling, briquetting or extruding, and toassociate the resulting pellets or balled-up masses of fines with theplus 14 mesh fraction being charged to the shafttype reducing furnace.In this latter connection, I have found that most low-grade startingmaterials contain an appreciable amount (a few percent) of a clay-likeplastic component, and that such component provides a very satisfactorybinder for the finesthereby making possible a'very much simplifiedprocedure for avoiding an unduly high content of fines in the chargecolumn, as follows. Where the starting material (when crushed)inherently produces a substantial amount of the fines but does notcontain an appreciable amount of said clay-like plastic component, Icrush the ore to about 1 inch, pass the entire crusher product through aballing drum (e.g., a balling drum such as that described in my US.Patent No. 2,831,210) wherein the finer particles agglomerate into smallballs or pelletswhich pellets give the same net effect as do the coarserpieces of the crusher productand charge the entire product of theballing drum to the ore column of the reducing furnace. This specialprocedure practically avoids the presence of fines in the column, makingfor uniform gas flow with a minimum of back pressure.

On some ores which are essentially rock-like and have little plasticityand, therefore, cannot be balled or extruded, I have found the fines canbe mixed with a small amount of cement-in the order of 5% by weightandthen briquetted and allowed to set for approximately 48 hours. At theend of this period these briquetted fines have acquired sufficientstrengths so that they can be charged along with the natural coarsematerial and little breakage will take place in the passage of thesebriquets through the furnace.

It should be appreciated that it is possible to use, as a source ofreducing gas, almost any of the common manufactured gases in which CO orH are the principal reducing agents. Natural gas which contains a highpercentage of CH; must be reformed into CO and H before it can beeffectively used. It is preferable, however, to use a gas containingsome CO rather than all H in order to maintain a favorable CO to CO+Hratio to prevent formation of FeO in the roasting operation. There isalso some advantage in having some CO in the reducing gas since thereaction of is exothermic which tends to maintain furnace temperatures.If only hydrogen gas is available the tendency to over-roast to FeO canbe largely minimized by introducing water vapor into the entrant gas tothe furnace.

From the standpoint of the apparatus aspect of the present invention, italready has been mentioned that the reducing furnace is of the shafttype. This shaft may be circular in cross-section, or it may be squareor rectangular in cross-section. For reasons to be discussedhereinafter, it is expedient in many cases so to design the shaftfurnace that its upper part is generally circular, while its lower partis rectangular, in cross-section.

The invention will now be described in greater particularity in thefollowing and in connection with the appended drawing, in which:

FIG. 1 is a schematic representation, in flow sheet form, of apparatusoperable for use in the cyclical reductive roasting process of theinvention;

FIG. 2 is a somewhat enlarged vertical sectional view of a reducingroasting furnace according to the invention, showing a particular formof apparatus for use in contributing heat to the reduction process;

FIG. 3 is similar to FIG. 2, and shows a modified form of reducingfurnace; and

FIG. 4 is a vertical sectional view of a form of reducing furnaceconstruction embodying principles for insuring uniform descent of theore column and for uniform distribution of cooling gas across thecross-sectional area of an ore column resident in the lower part of thecooling stove.

In FIG. 1, the reducing furnace per se is a substantially vertical shaftcomposed of a lower cooling'stove 4 and an upper heating stove 5.Heating stove 5 is provided at its top with a double bell-and-hopperfeeding means 6 for introducing feed ore into the furnace without lossof gas from the system, while cool-ing stove 4 is provided at its bottomwith a reduced ore product discharge means 3 for positively removingreduced and cooled ore from the reducing furnace, at controllablyvariable rates, without loss of gas from the system. Discharge means 3mayas shown-include a conventional star gate, or it may comprise anyother equivalent discharging device. At 7 there is schematicallyrepresented a wet dust collector-scrubber for cleaning and cooling spentcarrier gas exiting from the top of stove 5 by way of spent gas conduit8. Conduit 8 is provided with a valved vent means 9 for wasting toatmosphere a small (variable) fractional part of the total spent carriergas, and conduit 10 conducts the residual spent carrier gas to scrubber7. In scrubber 7 the carrier gas is cooled (e.g., to room temperature,60 F.) and the dust removed and excess moisture condensed out andexpelled together with excess C0 The so-conditioned carrier gas iswithdrawn from scrubber 7 through conduit 11 by,

means of blower 12, and by the latter is forced through cold carrier gasconduit 13. Conduit 13 delivers to two branch valved conduits 14 and 15which split the stream of cold clean carrier gas for delivery to inletconduit 2 and mixing chamber 17, respectively. A conduit 1 delieversactive reducing gas, produced in gas producer 18 and cleaned in scrubber19, to inlet conduit 2 for commingling therein with carrier gas toprovide an enriched gas. At 16 is indicated a burner means operable forburning fuel oil in a controlled amount of air to produce hot gaseouscombustion products devoid of free oxygen, for commingling in mixingchamber 17 with clean cold carrier gas delivered to mixing chamber 17through valved conduit 15. The hot carrier gas-neutral gaseouscombustion products mixture produced in charnber 17 is, through conduit20, introduced into the re ducing furnace, at a level adjacent thebottom of heating stove 5, and passes upwardly-in association withascending enriched gas (introduced at the bottom of cooling stove 4)with which latter it commingles-through that part of the total column orore resident in heating stove 5. In such passage said hot carriergas-neutral gaseous combustion products mixture gives up a major part ofits heat to the ore thereby heating the latter to desired reductiontemperature. The active reducing agent component of the enriched gas,for its part, becomes oxidized (to CO or/and H O, as the case may be) byreaction with the Fe O of the ore, and loses heat (acquired in passagethrough the ore in stove 4) to the ore in stove 5. The commingled gasesexit from the top of the furnace-through conduit 8-as the aforesaidspent carrier gas thus completing the gas cycle of the process.

FIG. 2 more specifically illustrates one form of furnace adapted for usein carrying out the process and including particular means for producingthe heating gas used for heating the ore to desired temperature foreffecting reduction of Fe O to Fe O According to this embodiment, thefurnace shaft, generally designated 30, is composed of, in series, agenerally cylindrical uppermost part 31; an elongated middle part ofwhich the upper portion 32 has the form of an inverted frustum of a coneand of which the lower portion 33' is generally cylindrical and hassubstantially the same cross-sectional area as that of uppermost part 31and of the apex end of portion 32; and a generally conical lowermostpart 34. The base end of the frusto-conical portion 32 has across-sectional area larger than that of uppermost part 31 and thejunction wall 37 joining the open bottom of part 31 with the base end ofportion 32 provides an annular free space 38 between the furnace Walland the periphery of a column of ore resident in the furnace. Parts 31,32 and 33 are constructed of the brick backed by heat-insulatingmaterial for conserving heat within the space enclosed by them: part 34suitably is constructed of sheet metal.

Junction wall 37 is provided with a plurality of down which latter leada plurality of valved branch conduits 45, 45, 46, 46. Branch conduits45, 45 communicate be tween bustle pipe 44 and the peripheral terminalbranches 50, 50 of a gas-distributing means 50, 51, 52 centrallydisposed within and adjacent the top of lowermost part 34, there beingas manyv branch conduits 45, 45 as there are terminal branches 50, 50(two each being shown in FIG. 2). In said gas-distributing means,branches 50, 50 extend radiallyoutwardly from a centrally (i. e.,axially) disposed multi-louvred gas distributor 51 the -1ouvres of whichare so arranged as to tend to direct gas under pressure radiallyoutwardly. therefrom and to distribute the same with substantialuniformity across the cross-section of a column of ore particlesresident in the lower part of cooling stove 4. A conical cap piece 52atop of distributor 51 permits the column of ore to passsmoothly overthe distributor. Branches 50, 50 may, if desired, be suit ably slottedto permit the discharge of part of the supplied conduit 2 may, as shown,be divertedthrough valved branches conduits 46, 46, to an annularchamber 55 surrounding said conical part adjacent the base of the cone.At its lower part annular chamber 55 merges into a conical vessel 56 thewall of which is spaced from and generally parallel to the wall ofconialpart 34 thereby providing a gas space therebetween for downwardpassage of cool gas (from annular chamber 55) over the surface of part34. Conical vessel 56 extends substantially beneath the lower edge 34'of conical part 34 and terminates in a generally cylindrical dischargetube 60 for delivery of cooled reduced ore from the furnace shaft to agaslocked product discharge means in communication with the open lowerend of said tube. Gas after passing through the space between parts 34and 56'discharges at the lower edge 34 into the ore. column about theperiphery of the latter.

Said gas-locked product discharge means includes a hopper 61 providedwith a gas-tight cover 62 through a. central orifice 63 in which covertube60 extends into the interior of the hopper. A slide valve means 65closes the bottom of the hopper and functions to deliver ore particles,from a constantly maintained supply thereof in the hopper, to beltconveyor means 66 for the forwarding of product to a point of use.

In this embodiment of the invention, the heating of the current of coldcarrier gas, provided through valved conduit 15, is effected in aneflicient manner. For this purpose, the generally cylindrical combustionchamber 16 has a diameter smaller than, and is axially disposed within,the generally cylindrical mixing chamber 17, the relative sizes of thetwo chambers being such that an annular space 70 is provided betweenthem, intothe lower part of which annular space gas is delivered from tocirculate about chamber 16 in passing into mixing chamber 17. A burner72 is axially disposed in the base of combustion chamber 16, said burnerbeing supplied with metered (or otherwise controlled) amounts offuel'oil and air through valved oil pipe 73 and valved primary air pipe74, respectively, for producing a supply of highly heated neutralgaseous combustion products. These latter stream through central opening76 in the top of the combustion chamber and into the main space withinmixing chamber 17 for thorough mixing with the carrier gas preheated inpassage through annular space 70.

The mixed gases pass through conduit into annular chamber 41.

Only one heating unit has been described above. However, it is preferredthat a pair of identical heating units be employed, the same deliveringhot mixed gas into annular chamber 41 at opposite sides of the furnaceshaft.

The heating units may be constructed somewhat more simply according tothe modification illustrated in FIG. 3. According to this modification,in each of the pair of heating units the combustion chamber 16 and themixing chamber 17 are series portions of a single horizontally disposedchamber separated one from the other by a partition wall 80 providedwith a central opening 76 for passage of highly heated gaseouscombustion products from combustion space into mixing space. Carrier gasis led into the latter at an opening 82 in the side wall thereof, forthorough mixing with the heating gas.

In this modified fonn, cold enriched gas, delivered by conduit 2, isdischarged into the ore column through a hooded discharge member 85.

Ore gravitating through conical lower part 34 passes into the tubularextension 88 and thence into closed vessel 89. This latter is dividedinto upper and lower portions by a generally horizontal aperturedpartition 90 through the apertures of which ore particles pass by theaid of a reciprocatory pusher device 91, 92. A supply of the oreparticles is maintained in lower part 93, the bottom of which latter isin communication with a star gate 94 of conventional form for dischargeof solids.

FIG. 4 illustrates a type of furnace peculiarly well adapted to handleores in which there may be some difficulty in material flow. In theroasting process the temperatures employed are well below the fusionpoint and thus no clinkering occurs. However, with certain ores, becauseof their physical nature and because of the amount of moisture or finespresent, it is sometimes desirable to incorporate in the design a seriesof rotating control shafts whose purpose it is to regulate the descentof the charge. These control shafts serve to break up any consolidatedmasses that have been formedthrough the packing of the material ratherthan through clinkering of the material-and to insure a uniform descentof the charge through the furnace which at the same time tends to insurea uniform flow of gas up through the shaft of the furnace.

In FIG. 4, as in FIG. 2, but one of the pair of identical heating unitshas been illustrated. Also as in FIG. 2, the external gas circuit hasbeen omitted as having already been shown in FIG. 1 and described inconnection with the latter.

According to this embodiment, the upper portion of the furnace shaft ismade circular in cross-section-thus making it possible to utilize thestructural advantages inherent in a circular design, and permitting theuse of a simple double bell-and-hopper device for feeding the orewhilstin the middle portion of the furnace shaft a conversion is made from acircular to a rectangular cross-section in order to make possible theinclusion of a series of horizontally disposed, parallel, rotatingbreaker shafts in the lower part of the cooling chamber or stove 4.Preferably, the conversion is a gradual one, starting from just belowthe level at which the heating gas is introduced into the furnace andextending to a level above the bank of breaker shafts above mentioned.

The breaker shafts extend across the rectangular part of the shaft andare journalled in bearings which are or may be incorporated into themasonry (brickwork) wall of the shaft, at least one end of each shaftextending exteriorly of the wall of the shaft and being provided at theexposed end with conventional means (not shown), e.g., a connection witha drive rod and crank arm therefor, actuated by a hydraulic cylinder andpiston, for oscillating the shaft. In lieu of such oscillating means,there may be used a rotating means including a drive shaft provided witha plurality of driving gears cooperating with driven gears keyed to theexposed ends of the shafts, said drive shaft being rotated by a variablespeed motor, preferably of the reversible type. Other conventional meansfor oscillating or rotating the breaker shafts may be used, it beingessential only that said means be adapted to being actuated at acontrolled variable rate of speed. Preferably, the actuation of all ofthe breaker shafts is effected at one side of the furnace and by asingle actuating means. The breaker shafts are provided, about thatportion of the periphery of each of them which is disposed between theopposite walls of the shaft, with spaced teeth arranged either in rowslongitudinally and radially of the shaft or helically about the shaft-orequivalent protuberances for positively augmenting the downward movementof the ore column.

In this embodiment, the cold (or, cool) enriched gas is introduced, byway of conduit 2, into the ore column by means of a plurality of spaced,parallel, louvered inverted trough-like gas distributors disposedadjacent to but below the bank of breaker shafts and between each pairof adjoining breaker shafts. Thereby, the enriched gas serves to coolthe breaker shafts, and is distributed uniformly over the cross-sectionof the ore column.

As is suggested above, a substantially dry ore of relatively coarsesize, and containing little fines, may not require the assistance of theabove-described breaker shafts in descending substantially evenlythrough the furnace, in-

which event the breaker shafts may be dispensed with: regardless of theexclusion or inclusion of breaker shafts in the organization, theabove-described means of distributing cool enriched gas throughout thecross-section of the ore column constitutes an important feature of thisembodiment of the invention.

In FIG. 4, an annular sloping baffle member 101 is incorporated in themasonry wall of the upper stove at a level adjacent to and above conduit8, which baffle member extends inwardly and downwardly to form, with theshaft wall, an annular gas-collecting space 102 with which the inner endof conduit 8 communicates. Similarly, annular bafile 103 is provided ata level adjacent to and above conduit 20, which bafiie extends inwardlyand downwardly to form, with the shaft wall, an annular plenum space 104from which heating gas-supplied through conduit 20is forced into the orecolumn.

A plurality (four illustrated in the drawing) of horizontally disposed,spaced parallel breaker shafts 110, 110 extend across the rectangularpart of stove 4, to the exposed ends 112, 112 of which are attachedconventional means (not shown) for oscillating the breaker shafts. aboutthe periphery of each breaker shaft is disposed an array of spaced teeth113, 113 which-when the breaker shafts are moved-engage the particles ofthe ore column, loosen the ore and (their primary function) break up anyagglomerated masses or chunks of material which may have formed. Thespacing between the toothed shafts is such that all particles other thansaid chunks freely pass between them regardless of whether or not theyare being rotated.

Disposed closely beneath breaker shafts 110, 110 and parallel with thelatter, are spaced, parallel, inverted trough-like gas distributors(three shown) 120, 120 the sloping sides of which are louvered (as shownat 121) to provide an array of gas inlet means making for extensivedistribution of gas across the cross-section of the rectangular part ofstove 4. Gas from conduit 2 enters the trough-like gas distributors byway of branch pipes 122, 122 communicating between conduit 2 and theinterior of members 120, 120. As is illustrated in FIG. 4, the number ofgas distributors 120, 120 is one less than the number of breaker shafts110, 110, and each gas distributor is positioned between (and justbeneath) each pair of adjacent breaker shafts, whereby cool gas isdirected onto the breaker shafts and into the loosened ore particlesmoving past said shafts andis uniformly distributed throughout thecross-section of the ore column.

The process will now be described in further detail and exemplified bythe following specific examples.

Example I Percent Fe O 55.0 SiO 41.5 A1 1.2

As received, moisture content 6%.

Batch tests indicated that this ore could be satisfactorily reductivelyroasted after crushing to pass a 1 inch square opening.

The ore wa crushed to this size and, without further sizing, was fed tothe reductive roasting furnace schemati cally represented in FIG. 1.

The apparatus had the following dimensions: upper cylindrical stove 5had an inside diameter of 9 feet. Ore was charged, at 6, at the rate of25.44 gross (long) tons per hour, at 60 F.

The blower 12 forced 818.0 #/minute of cold, clean, spent carrier gas,delivered to it by conduit 11 from the It) scrubber 7, through the coldgas conduit 13, this gas having the following composition:

#/Inin. Percent Reducing gas used in this example was made from coke ina slagging type gas producer 18, and, after being scrubbed at 19, wasforced through conduit 1, this gas having the following volume andcomposition:

#lmin Percent The re-circulating carrier gas was split into twoportions. One portion was diverted into conduit 15 and the other portioninto conduit 14. The gas in conduit 14 and conduit 15 had the followingcomposition and volumes:

Percent Conduit 14, Conduit15,

#lrnin. #lmin.

The carrier gas from conduit 14 and the reducing gas from conduit 1commingled in conduit 2' to produce an enriched carrier gas of thefollowing composition and This enriched carrier gas entered the orecolumn in lower stove 4, where it recovered heat from the ore, andascended into the upper ore column in upper stove 5. As it entered thelatter, it commingled with the gas from mixing chamber -17.

In mixing chamber 17, 248.5 #/min. of gas from conduit 15 was mixed withthe hot (1000 F.) gaseous combustion products, analyzing #lmin. PercentTotal 60. 5

issuing from the combustion chamber 16 appurtenant to the mixingchamber, in which combustion chamber fuel #lmin Percent 85. 8 8. 8 37. 13v 8 0. 0. 0 S31. 4 85. 3 20. 8 2. l

In order to keep the system from increasing in pressure, a vent means 9'was provided to keep the system in balance. The minimum top gas wastedto atmosphere was 12.5%, based on a nitrogen balance. This percentagevaried somewhat with temperature, moisture content, and 00" content.

The remainder of the spent gases passed into a wet dustcollector-scrubber 7 where the same was cooled and the excess moisturecondensed out and expelled together with the excess CO over and beyondthat accumulating in the system for equilibrium while maintaining anitrogen balance. The volume and composition of these top gases were asfollows:

Of these gases 12.5% were wasted to atmosphere by the vent means(conduit 9) and-87.5% passed to the scrubber (conduit 10).

The heat requirements of the above system were such that 201,000Btu/min. were required to heat the ore from 60 F. to 1,000 F.; 67,000Btu/min. were required to evaporate the moisture to dehydrate the ore;and 10,000 B.t.u./ min. were necessary to compensate for radiationlosses, for a total of 278,000 B.t.u./min.

The heat sources were: 44,000 B.t.u./min. from the exothermic reaction;160,000 B.t.u./min. were recovered by the ascending gases; and 74,000B.t.u./min. were supplied by combustion of fuel oil at the combustionchamber.

The heat losses from the reducing furnace were:

B.t.u./ min.

Radiation 10,000 Heat in rejected ore 41,000

Heat in top gases of which 67,000 was for dehydration of ore 227,000

Total 278,000

The ore as fed to the furnace had a temperature of 60 F. In the upperstove 5 of the furnace it was heated to a maximum temperature of10001600 F., and was cooled to approximately 260" F. in passage throughthe lower stove f the furnace; Ore was discharged, at 3, at the rate of23.82 l.t./hr. and at the discharge temperature of 260 F.

It is of interest that ofthe total gas blown into the reducing roastingfurnace approximately 65% was introduced, into the ore column, adjacentthe reduced ore product discharge 3 to cool the descending (hot) oredown to an exit temperature of approximately 260 F. Even at thisrelatively low temperature there was some danger of reoxidizing themagnetite formed from the 12 hematite in the roasting operation. rate ofdischarge through 3- was controlled by means of a star gate and thematerial was discharged under water in a spiral type classifier.

All of the heat to the system was supplied by burning fuel oil in theDutch oven combustion chambers 16- within the mixing chambers (one,only, of which has been indicated in the flow sheet). The procedure inburning the fuel oil with no excess of oxygen made it possible to burnthe oil completely and effectively and to reduce radiation losses.

The quenched discharged ore from 3 was ground, in a 9 ft. by 12 ft. ballmill to all minus 100 mesh, and then was concentrated magnetically onthree, three-drum rotary wet magnetic separators.

RESULTS OF CONCENTRATION TESTS In this example, the starting materialwas ore identical in analysis, and structure, to that used in Example 1.

The apparatus was essentially the same as that used in Example 1, andthe ore was charged to it at the same rate of 25.44 gross (long) tonsper hour.

The blower 12 forced 869.8 #/minute of cold, clean, spent carrier gasthrough the cold gas conduit 13. This 38 gas had the following amountsand composition:

#lmin. Percent Reducing gas, made in a Wellman-Galusha type of gasproducer using coal as a fuel, was forced through conduit 1. This gashad the following composition:

#1111111. Percent Total 16.02

The re-circulating carrier gas was split into two parts. One part wasdiverted to conduit 15 and the residual part into conduit 14. The gas inconduits 14 and 15 had the following composition and volumes:

The carrier gas from conduit 14 and the reducing gas from conduit 1commingled in conduit 2 to produce an Consequently, the

enriched carrier gas of the following amount and composition:

This enriched carrier gas entered the ore column in lower stove 4 whereit recovered heat from the ore and ascended into the upper ore column(stove 5). As it entered, it commingled with the gas from mixing chamber17. This mixture of gases had the following amount and composition:

#lmin. Percent C Or 96. 5 9. 4 C O 9. 7 0. 9 H: 3. 7 0. 4 N2 896. 8 87.1 H20 22. 3 2. 2

Total 1029. 0

In order to keep the system from increasing in pressure, the vent 9 wasused to keep the system in balance. The minimum top gas waste toatmosphere was 5.8% based on a nitrogen balance. This percentage wouldvary with temperature, moisture content, and CO content.

The remainder of the spent gases passed into wet dust collector-scrubber7 where they were cooled and the excess moisture was condensed out andexpelled together with the excess CO over and beyond that accumulatingin the system for equilibrium while maintaining a nitrogen balance.

The amount and composition of these top gases, prior Of these gases 7.5%exited through the vent (conduit 9) and 88.4% passed to the scrubber 7(conduit 10).

The heat requirements of the above system were such that 201,000B.t.u./min. were required to heat the ore from 60 F. to 1,000 F.; 67,000B.t.u./min. were required to evaporate the moisture and to dehydrate theore; and 10,000 B.t.u./min. were needed to meet radiation losses for atotal of 278,000 B.t.u./min.

The heat sources were: 31,000 B.t.u./rnin. from the exothermic reaction;160,000 B.t.u./min. were recovered by the ascending gases; and 87,000B.t.u./min. were supplied by combustion of fuel oil at the combustionchamber.

The heat losses from the reducing furnace were:

Btu/min. Radiation 10,000 Heat in rejected ore 41,000

Heat in top gases of which 67,000 is for dehydration of ore 227,000

Total 278,000

The quenched, discharged ore from 3--23.82 l.t./hr.-- was ground in aball mill to all minus 100 mesh, and was then concentrated magneticallyon a series of three threedrum rotary wet magnetic separators.

RESULTS OF CONCENTRATION TESTS Example 2 Product Percent Percent PercentPercent weight iron silica total iron Crude ore 100.00 38.46 41. 55100.00 Roasted ore 95. 32 4o. 35 43. 59 100. 00 Magnetic concentra 55.29 64. 62 6. 46 92. Non-magnetic tailing 40. 03 6. 84 7. 10

This application is a division of application Serial No. 763,348, filedSeptember 25, 1958, now US. Patent No. 2,931,720.

I claim:

Apparatus for use in carrying out a cyclical process of reductivelyroasting initially substantially non-magnetic iron ore material by meansof a gas mixture consisting essentially of non-oxidizing neutral gasesincluding carbon dioxide and an active reducing gas selected from thegroup consisting of carbon monoxide, hydrogen and a mixture of carbonmonoxide and hydrogen, the content of carbon dioxide being several timesthat of said active reducing gas, said apparatus including asubstantially gas-tight, generally straight-walled and verticalshaft-type furnace; means for feeding ore material into said furnace andonto the top of a column of such ore material resident in said furnace;annular means cooperating with the wall of said furnace and with anupper surface of such ore column to define an annular upper free spaceabove such column for collection of spent gas exiting from such column;annular means cooperating with the wall of said furnace and with theperiphery of such column intermediate the top and the bottom of thelatter to define an intermediate free space; gas delivery means adjacentthe bottom of said furnace; ore discharge means at the bottom of saidshaft; a gas-scrubbing and cooling means; a discharge conduitcommunicating between said annular upper free space and saidscrubbing-cooling means, said discharge conduit including valved meansfor venting spent gas to atmosphere; a blower; a conduit communicatingbetween said scrubbing-cooling means and the intake side of said blower;an active reducing gasproducing means; a gas-mixing chamber; acombustion chamber housing a fuel burner and in communication with saidmixing chamber for delivering into the latter a high-temperature neutralheating gas; a branched delivery conduit leading from the output side ofsaid blower, a first branch of which delivers scrubbed and cooled spentgas to said mixing chamber and a second branch of which is incommunication with said gas-producing means, delivers cool enriched gasto said gas delivery means; and a conduit communicating between saidmixing chamber and said intermediate free space for delivering to thelatter a current of hot, substantially neutral gas mixture underpressure, the apparatus being further characterized in that saidcombustion chamber and said mixing chamber are generally cylindrical, inthat said mixing chamber is longer, and has a greater diameter, thansaid combustion chamber, in that said combustion chamber is disposedco-axially within an end portion of said mixing chamber there being anannular open heating space between the side wall 'of said combustionchamber and the side wall of said mixing chamber with which annular openheating space said first branch of said delivery conduit communicates,said combustion chamber sharing an end wall with said mixing chamber andsaid end wall being provided with an aperture in which said fuel burneris mounted, and in that said combustion chamber is pro- 15' videdwith anaxial opening for discharging hot gaseous 2,343,780 Lewis Mar. 7, 1944combustion products into that part of said mixing cham- 2,670,946Royster Mar. 2, 1954 her in which said combustion chamber is notlocated. 2,785,063 Haley et a1. Mar. 12, 1957 I 2,799,491 Rusciano July16, 1957 References Cited in the file of this patent 5' 6 0 D6 Iahn Dec.2, 1958 UNITED STATES PATENTS FOREIGN PATENTS 2,124,764 Comstock July26, 1938 680,605 Germany Sept. 1, 1939

